MB-8325 Adapt system_stats_collector to latest portsigar changes.

Change-Id: Ibde1162c266ceb3d9c150ff88064217f7ff71eef
Reviewed-on: http://review.couchbase.org/26434
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8325 Send processes' stats with heartbeat.

Change-Id: Ie243e48772a039b73f47e0b73283fb7d645e19da
Reviewed-on: http://review.couchbase.org/26435
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>